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A Holistic Sustainable Approach to Small-Scale Water Desalination in Remote Regions: Development of a thermal desalination method based on vapour transfer processes in water-filled bubble columns

Schmack, Mario (2015) A Holistic Sustainable Approach to Small-Scale Water Desalination in Remote Regions: Development of a thermal desalination method based on vapour transfer processes in water-filled bubble columns. PhD thesis, Murdoch University.

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This thesis describes the development of a novel thermal desalination process based on the vapour transfer processes occurring in a water-filled bubble column. A strong focus on facilitating the involvement of local people and on promoting local capacity building by utilising simple technologies steers the research towards thermal desalination. The problem is addressed by first identifying alternative and previously unused water sources that can be utilised for sustainable water provision in remote places. The experimental analysis of a new desalination concept that combines a bubble column evaporator with a simple passive flatplate copper condenser is then provided. A comprehensive condenser assessment under a range of different physical conditions that examine the effects of external water cooling, partial insulation and aspects of air circulation on condenser performance is presented. Subsequently, for the purpose of mitigating high bubble column vapour temperatures without risking greenhouse plant survival in a prospective Bubble-Greenhouse, an alternative set of cooling and pre-condensing devices is assessed. Based on the findings, a conceptual Bubble-Greenhouse design that promotes a holistic sustainable approach to combined water provision and community development is then described.

A prototype bubble evaporator is quantitatively and qualitatively assessed for the consistency of its performance and demonstrates a steady evaporation rate. The resulting data provides the basis for extrapolation of bubble evaporator capacity, both for relatively small standalone systems and for significantly up-scaled components that would operate in a Bubble-Greenhouse. In passive mode, condensate recovery rates of around 73% are achieved without the need for external cooling. Estimated by extrapolation, a standalone bubble desalination system with a 1m2 condenser may produce around 19 litres of distilled water per day. The common feature of the alternative set of cooling and pre-condensing devices is that they are easy to manufacture, of low energy demand and low investment cost and technically and operationally appropriate for local people in remote places. Under laboratory conditions, the passive copper tube concepts achieve water recovery rates of between 65-75% and the air cooled bubble condenser columns achieve condensate recovery rates of at least 50%. However, it emerges that a well designed latent heat recovery system is required to keep the energy demand of a thermal desalination system within acceptable limits, both technically and financially. Although the stacked evaporator-condenser bubble column array cannot demonstrate a significant cooling and condensing advantage over the flat-plate condenser, the concept facilitates the implementation of a heat recovery cycle. This attribute ultimately leads to the multistage evaporator-condenser module concept with an effective latent heat recovery system that is integrated into the horizontally stacked chambers, a key element of the Bubble- Greenhouse technology. The greenhouse desalination system is designed with a water production capacity of 8m3 per day. Due to the strongly reduced water demand of plants inside a humidified greenhouse, only a fraction is required for irrigation and the bulk of water is intended for human consumption.

This study aims to contribute to the field of water service provision in remote communities, particularly by improving some of the shortcomings of conventional high-tech water treatment technologies that often fail in these situations. A comprehensive discussion posits the Bubble-Greenhouse concept in the context of these remote community water provision shortcomings and highlights how the proposed new treatment method aims to alleviate these. Consequently, the findings presented here may help to inform the essential transition from externally-led water service provision towards a self-determined community operated service, recommendations for future research and recommendations for implementation of a Bubble- Greenhouse field trial conclude the thesis.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Engineering and Energy
Supervisor(s): Ho, Goen and Anda, Martin
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